Evaluating contributions of hatchery-origin fish to conservation of endangered Sacramento River winter run Chinook salmon during a drought

Hatchery-reared fish have been used to supplement endangered winter-run Chinook salmon in the upper Sacramento River since 1989. Intense drought in the past five years has led fisheries managers to substantially modify their hatchery protocols, increasing the total number of fish released and using hatchery-origin adults for producing juveniles. The influence of the hatchery-reared fish and the subsequent drought-hatchery practices on the winter-run Chinook population are not yet fully understood. This study aims to address this knowledge gap and inform the best practices for using hatchery-reared Chinook in conservation actions.

This project will evaluate multiple aspects of how hatchery–reared fish contribute to natural production of winter-run Chinook salmon in the upper Sacramento River, providing critical information on the impacts of drought related management actions. Specifically, researchers will:

Assess whether hatchery-reared fish produce returning offspring when they spawn in the wild and determine if the relative contribution of hatchery fish to the population is influenced by the drought;

Assess potential differences in reproductive success among hatchery and natural origin fish before and after the onset of the drought;

Use standard genetic measures of population demographics to better understand the genetic diversity of the population and the influence the hatchery-reared Chinook may have on overall genetic diversity before and during the drought;

Determine if signals of adaptation to captivity in the hatchery population are occurring due to the drought protocols.

This research will be used by the Bay Delta Office of the US Bureau of Reclamation and fisheries managers to assess recent management decisions and help inform future management actions. It will also give managers and scientists a set of genetic tools they could use to inform best conservation practices using hatchery fish supplementation.